How to pass randomly-generated data to include_tikz in R/exams?

Question

When I add static data to a chart created with TikZ and include_tikz() from R/exams, they are rendered correctly. For example I have created the following graphic

TikZ graphic

using exams::include_tikz(graf01, library = "arrows") with the TikZ code below. And then I can include it in exams2html(), exams2moodle(), etc.

 graf01<-c("\definecolor{uuuuuu}{rgb}{0.26,0.26,0.26}",
      "\definecolor{zzttqq}{rgb}{0.6,0.2,0}",
      "\definecolor{ududff}{rgb}{0.30,0.30,1}",
      "\begin{tikzpicture}[line cap=round,line join=round,>=triangle 45,x=1cm,y=1cm]",
      "\clip(-0.1,-0.1) rectangle (5,5);",
      "\fill[line width=2pt,color=zzttqq,fill=zzttqq,fill opacity=0.10] (0,0) -- (4.68,-0.02) -- (4.7,4.66) -- (0.02,4.68) -- cycle;",
      "\draw (3.44,3.80) node[anchor=north west] {\textbf{12}};",
      "\draw (0.35,4.57) node[anchor=north west] {\textbf{DH}};",
      "\draw (3.97,4.57) node[anchor=north west] {\textbf{CA}};",
      "\draw (2.31,0.72) node[anchor=north west] {\textbf{R}};",
      "\draw [line width=2pt] (1.76,3.08) circle (1.3cm);",
      "\draw [line width=2pt] (3.05,3.13) circle (1.3cm);",
      "\draw [line width=2pt] (2.45,1.98) circle (1.3cm);",
      "\draw [line width=2pt,color=zzttqq] (0,0)-- (4.68,-0.02);",
      "\draw [line width=2pt,color=zzttqq] (4.68,-0.02)-- (4.7,4.66);",
      "\draw [line width=2pt,color=zzttqq] (4.7,4.66)-- (0.02,4.68);",
      "\draw [line width=2pt,color=zzttqq] (0.02,4.68)-- (0,0);",
      "\begin{scriptsize}",
      "\draw [fill=ududff] (0,0) circle (2.5pt);",
      "\draw [fill=ududff] (4.68,-0.02) circle (2.5pt);",
      "\draw [fill=uuuuuu] (4.7,4.66) circle (2.5pt);",
      "\draw [fill=uuuuuu] (0.02,4.68) circle (2.5pt);",
      "\end{scriptsize}",
      "\end{tikzpicture}")

Now instead of hard-coding the number 12 in graf01[7]

"\draw (3.44,3.80) node[anchor=north west] {\textbf{12}};"

I want to use a randomly-generated number, say:

 vald <- sample(1:20, 1)

I tried using

"\draw (3.44,3.80) node[anchor=north west] {\textbf{vald}};"

but then the string vald instead of its value is included:

How can I include the value of vald instead?

user_4233642 · Answer

To include the value of a variable in a string you can use the function paste() or paste0():

vald <- 7
line7 <- paste0("\draw (3.44,3.80) node[anchor=north west] {\textbf{", vald, "}};")
line7
## [1] "\draw (3.44,3.80) node[anchor=north west] {\textbf{7}};"

Or for equivalent output sprintf():

line7 <- sprintf("\draw (3.44,3.80) node[anchor=north west] {\textbf{%s}};", vald)

The latter is typically more convenient if you have several placeholders like %s in a string or when you have different types of placeholds etc.

In either case you can subsequently do:

graf01[7] <- line7
include_tikz(graf01, library = "arrows")

How to pass randomly-generated data to include_tikz in R/exams?

1 Answers